1. Field of the Invention
This invention pertains to an optical switch used in the switching of optical transmission lines.
2. Description of the Related Art
In Patent Reference 1 and Patent Reference 2, there are reported optical switches using MEMS (Micro Electro Mechanical Systems) techniques of a type with two inputs and two outputs and a type with one input and three outputs.
In case the input light is switched to two outputs, it is possible to provide these optical switches for that use, but it is appropriate to prepare a device composed of one input port and two output ports for the purpose of miniature integration. In that case, it is further in particular optimal, for the purpose of intensive use of space, to choose a device having a structure in which the three ports are all lined up on one side of a chip.
In FIG. 2B of Patent Reference 3, there is described an example of a MEMS optical switch having such a structure. However, this configuration has the optical path lengths which are not the same going from the switch-related input port respectively to the two output ports, so the conditions of the two optical paths are unbalanced and output light of the same optical quality cannot be obtained from the two output ports.
Generally, in an optical switch, it is desirable for the intensity, spot size, polarization properties and the like of the switched output lights to be all uniform among the output port. To that end, it is a condition that the optical propagation conditions of the switched optical paths are equivalent. Accordingly, in the case of an optical switch with one input and two outputs, if two switchable optical paths are configured to be completely symmetric, including the disposition and the angle, optical distance, and collimator parts, etc., the aforementioned conditions are completely satisfied in an ideal way. Also, even if two optical paths cannot be configured to be completely symmetric, by at least making the optical distances thereof coincide and the mirror angle relationships equivalent, it is possible to equalized the two output lights regarding the intensity and spot size, as well as the polarization properties.
Further, in FIG. 3 of Patent Reference 3, there was described an example of an optical switch with a structure in which the three ports are all lined up on one side and yet, the optical paths of both output ports are uniform, but this is a switch utilizing a rotating mirror, and it is not possible to obtain a bistable operation etc. in the moving parts.
Also, according to a conventional device, described in Patent References 1 to 3, with a structure inserting and pulling out a moving mirror into/from the optical path, and switching and utilizing the reflection and transmission thereof, the moving mirror must first, in the case of utilizing reflected light by inserting a moving mirror in the optical path, be completely inserted in the optical path with a sufficient actuation distance, and the residual transmitted light, i.e. the crosstalk to the transmission port, must be sufficiently blocked and brought to extinction. Moreover, in the case of pulling out the moving mirror and utilizing the transmitted light, the moving mirror must be completely pulled out, by the sufficient actuation distance only, from the optical path, and the crosstalk of the residual reflected light arising from the fact that one part of the mirror slightly blocks the optical path must be sufficiently brought to extinction. In the conventional device, it was in the end imperative, in order to satisfy the isolation specification, to take each sufficient actuation distance, the former and the latter, to be the stroke and to actuate each moving mirror.
Patent Reference 1: Japanese Patent Application Laid Open No. 2005-37885.
Patent Reference 2: Japanese Patent Application Laid Open No. 2000-111815.
Patent Reference 3: Japanese Patent Application Laid Open No. 2001-201699.
Patent Reference 4: Japanese Patent Application Laid Open No. 2003-43270.
Patent Reference 5: Japanese Patent Application Laid Open No. 2004-125899.